As one kind of field effect transistors (FETs), an existing TFT has a wide range of application.
Generally speaking, the TFT includes a gate electrode, a gate insulating layer, a semiconductor layer, a source electrode and a drain electrode. Conductivity of a channel layer may be adjusted by changing a voltage applied to the gate electrode, so as to control on and off states between the source electrode and the drain electrode.
For an N-type TFT, when a voltage applied to its gate electrode is greater than a threshold voltage, an on state is formed between its source electrode and its drain electrode; otherwise, an off state is formed between its source electrode and its drain electrode. For a P-type TFT, the contrary is the case, i.e., when a voltage applied to its gate electrode is less than a threshold voltage, an on state is formed between its source electrode and its drain electrode; otherwise, an off state is formed between its source electrode and its drain electrode. Hence, a size of the voltage applied to the gate electrode depends on the threshold voltage.
Therefore, when the TFT serves as a switching transistor, it is impossible to switch between on and off states for the source electrode and the drain electrode accurately due to the threshold voltage drift.
For an active matrix organic light-emitting diode (AMOLED) pixel circuit, brightness evenness of OLED may be adversely affected by a change in the threshold voltage of the TFT which serves as a driving transistor, thereby adversely affecting display effect of an AMOLED panel.
Hence, no matter in which kind of circuit structures the TFT is used, normal operations of the circuit structure may be adversely affected by the threshold voltage drift of the TFT.